Gas turbine efficiency generally increases with the temperature of the combustion gas stream. Higher combustion gas stream temperatures, however, may produce higher levels of undesirable emissions such as nitrogen oxides (NOx) and the like. NOx emissions generally are subject to governmental regulations. Improved gas turbine efficiency therefore must be balanced with compliance with emissions regulations.
Lower NOx emission levels may be achieved by providing for good mixing of the fuel stream and the air stream. For example, the fuel stream and the air stream are premixed in a Dry Low NOx (DLN) combustor before being admitted to a reaction or a combustion zone. Such premixing tends to reduce combustion temperatures and NOx emissions output. Other systems attempt to reduce flame holding by inserting diluents into the fuel-air mixture so as to achieve a predetermined mixture and/or temperature.
Premixing, however, also may cause or promote auto-ignition, flashback, flame holding and/or other types of performance issues. Specifically, flame holding may be impacted by the non-uniformity in the fuel and the air streams due to the incoming profile. Further, flame holding also may be an issue with fuel jet interaction within the nozzle.
There is therefore a desire for a premixer to provide good fuel-air mixing so as to increase overall efficiency and flame holding margin while complying with emissions regulations. Preferably such a premixer may be used with new and existing equipment.